1. Field of the Invention
In recent years considerable attention has been given to the roller applicator for applying solutions of herbicides for the control of weeds growing amongst field crops. It is particularly useful late in the season for eradicating weeds and other volunteer plants protruding above the crop canopy and posing a problem during harvest. The roller applicator is designed to selectively dispense herbicide solution to the target plants by direct contact with an absorbent roller. The most common type utilizes carpet as the absorbent covering and is thus commonly referred to as a "carpet roller." A major problem with carpet rollers has been maintenance of the proper level of surface moisture for weed control. Drippage of the saturated carpet is minimized by continuous turning of the roller. When the roller is stopped, excessive drippage onto crops occurs due to the extensive fluid retained in the carpet material. This results in both crop damage and waste of herbicide. Emulsions and suspensions of wettable powders are not practical to use with carpet rollers because of phase separation induced by the filtering effect of the fiber pile. Likewise, the fibers can induce a salting-out of some formulations. Both types of separation result in a reduction in the effectiveness of the herbicide and a buildup of residue in the carpet, thereby limiting carpet rollers for use with only soluble materials. The present invention relates to a roller applicator which resolves these difficulties.
2. Description of the Prior Art
The problem of moisture control on carpet rollers has been addressed by Bertness (U.S. Pat. No. 4,253,272), Burnside (U.S. Pat. No. 4,223,479), and Schepers et al. (U.S. Pat. No. 4,265,048). In each of these patents, the moisture content of the roller is monitored as a function of an electrical value, and a system responsive to that value controls subsequent wetting of the carpet. Despite limited effectiveness of such systems, carpet rollers nonetheless remain susceptible to the aforementioned separation and cleaning problems. Keeton (U.S. Pat. Nos. 4,346,531 and 4,347,684) discloses an applicator in which the roller comprises a bare, hard plastic tube. A similar arrangement is taught by Lohoar in U.K. Pat. No. 2,083,732. However, in each case, absorbent materials are used to transfer liquid from the storage reservoir to the roller, thereby preempting any advantage relating to cleaning and avoidance of phase separation.